Obtaining optical properties of skin leads to useful information about the skin physiology, morphology, and composition. These can be obtained in a non-invasive manner and in real time using an optical method of analysis. One such optical method is reflectance spectroscopy consists of two components: specular reflectance and diffuse reflectance. The specular reflectance of a skin sample is the light which does not propagate into the sample, but rather reflects from the front surface of the sample. This component contains information about the biological sample at the surface. In order to gather information from the deeper section of the biological tissues, diffuse reflectance spectroscopy can be applied.
Diffuse reflectance spectra are obtained from the light that has traveled within the tissue. As the beam penetrates the biological tissue, the direction of propagation changes randomly due to the refractive index variations in the layers beneath. The light is attenuated on its pathway due to the absorption and scattering events. After numerous scattering events, some of the light emerges from the surface. The intensity of this reflected light carries information regarding the absorption and scattering of light through the medium which can be correlated with the morphology to determine the pathological state of the tissue and/or the concentration of a biochemical/analyte in the tissue. Diffuse Reflectance Spectroscopy has been widely used for non-invasive analysis and the characterization of the biological tissues. This technique provides rapid quantitative measurements of pigments within the tissue. Non-invasive measurements via reflectance spectroscopy are desirable because they are painless, do not require fluid drawn from the body, carries little risk of contamination or infection, and do not generate any hazardous waste and enables rapid measurement. Accurate, non-invasive determination of bilirubin, as an example, could reduce many of the complications associated with the newborn jaundice. Similarly, accurate, non-invasive determination of various disease states could allow faster, more convenient screening and diagnosis, allowing more effective treatment. Biomedical applications of reflectance spectroscopy include study on colon, esophagus, stomach, bladder, cervix, ovaries, breast, brain, liver, pancreas, heart, oral tissues, and skin.
A typical measurement setup for reflectance spectroscopy consists of a light source for illumination of skin, a detector for evaluation of reflected light, and an optical probe for delivery and collection of the reflected light. A light source can be a halogen lamb a tungsten lamb, a light emitting diode (LED) etc. A detector can be a photo detector or a spectrometer. Generally, fiber optic cables are being used as an optic probe for light transmission. Optic probes consist of two separate light paths, one for the delivery of light to the targeted biological tissue and one for the collection of light coming from the targeted biological tissue.